Conductive composite fiber

ABSTRACT

A conductive composite fiber is formed from a polymer containing conductive carbon black in a polyamide resin as a conductive layer and thermoplastic resin as a nonconductive layer that is exposed in three or more locations on the outside surface of the fiber in a cross section, the coefficient of variation in the surface area of each conductive layer in a fiber cross section is 10% or less, and the average value of the area specific resistance is 4 log (Ω·cm). The variation in the fiber surface specific resistance is suppressed and the variation in the exposed surface area of each conductive layer polymer in a fiber cross section is suppressed by exposure of the conductive layer in three or more locations on the fiber surface, crimping of the original yarn is suppressed by equal disposition, and antistatic performance for woven and knitted fabrics and carpets is improved.

TECHNICAL FIELD

This disclosure relates to a conductive composite fiber having excellentstatic elimination performance. More specifically, the disclosurerelates to a conductive composite fiber in which the variation in thefiber surface specific resistance and the variation in areas ofconductive layers in a fiber cross section is suppressed by exposure ofthe conductive layers at three or more locations on the fiber surface,crimping of the original yarn is suppressed by equal disposition, andantistatic performance for woven and knitted fabrics is improved.

BACKGROUND

Conventionally, various proposals have been made for conductive fibersas fibers having excellent static elimination performance. Examples ofthe proposals include plating the surface of nonconductive fibers with ametal to provide conductivity, and dispersing a conductive carbon blackin a resin or rubber and then coating the fiber surface with the resinor the rubber to form a conductive coating layer. However, there is aproblem that the conductive fibers are of no practical use because themethods to obtain the conductive fibers are technically difficult due tothe complicated manufacturing process, and because the conductivity iseasily deteriorated in the preparation stage for practical use of theconductive fibers, for example, in the chemical treatment in thescouring process for weaving and knitting, or by external actions ofwear, repeated washing and the like in actual use.

As other conductive fibers, metal fibers such as steel fibers are knownto have excellent static elimination performance. Metal fibers are,however, expensive and difficult to match with general organic materialsso that metal fibers easily have poor spinning performance, causeproblems in processes of weaving, and dyeing and finishing, causebreaking and falling due to washing when worn, and also cause problemsof electric shock and sparking due to electrical conductivity, troublein fabric melting and the like.

In addition, a method of fiberizing a polymer in which a conductivecarbon black is uniformly dispersed to obtain another type of conductivefiber has been proposed. However, because the conductive fiber containsa large amount of carbon black, manufacturing the conductive fiber isdifficult, the cost is high, and the physical properties of the fiberare remarkably deteriorated so that there is a problem that it isdifficult to manufacture products unless special processes are used. Asa proposal to solve the problems, for example, in Japanese PatentLaid-open Publication No. 52-152513, a fiber in which a conductivepolymer layer containing conductive carbon and a nonconductive polymerlayer containing the same polymer and no conductive carbon are laminatedtogether in a multilayer shape is proposed for the purpose of improvingdurability, mainly for the purpose of improving static eliminationperformance and preventing exfoliation between the component layers.Also in the fiber, however, the layer containing a conductive carbonblack is exposed too much on the surface so that improvement in chemicalresistance and durability is not recognized.

Furthermore, proposals have been recently made in Japanese PatentLaid-open Publication Nos. 2003-278031 and 2004-36040 and InternationalPublication No. 2007/046296 to improve conductive performance byexposure of a conductive layer on the outside surface of the fiber in afiber cross section. For example, JP '031 provides a conductive fiberhaving an excellent static elimination effect and static eliminationdurability obtained by exposure of conductive layers at four or morelocations on the outside surface of the fiber in a fiber cross sectionand by substantially equal disposition of conductive layers.

In the conductive fiber proposed in JP '031, it is difficult to exposelocally without variation and dispose equally a minute amount of polymerhaving poor fluidity and containing conductive fine particles, and thestatic elimination performance is not at a satisfactory level.Similarly, in the conductive composite fibers proposed in JP '040 and WO'296 in which the conductive layer portion is partially exposed on thefiber surface, the coefficient of variation (CV %) in the area exposedon the surface of conductive layers in a fiber cross section is large,and the variation in the disposition of conductive layers is also causedso that there is a problem that a stable static elimination effectcannot be obtained because wave-like crimping is caused in thelongitudinal direction of the yarn.

It could therefore be helpful to provide a conductive composite fiberthat cannot be sufficiently achieved by conventionally known conductivecomposite fibers, in which the variation in the area of the polymer inconductive layers in a fiber cross section is suppressed, and crimpingof the original yarn is suppressed by accurate equal disposition, andantistatic performance for woven and knitted fabrics is improved.

SUMMARY

We thus provide:

(1) A conductive composite fiber containing: a polymer as conductivelayers, the polymer containing a polyamide resin containing a conductivecarbon black; and a thermoplastic resin as a nonconductive layer,wherein the conductive layers are exposed at three or more locations onan outside surface of the conductive composite fiber in a fiber crosssection, a coefficient of variation (CV %) of areas of the conductivelayers in a fiber cross section is 10% or less, and the conductivecomposite fiber has an average value of a volume specific resistance of4 log (Ω·cm) or less.(2) The conductive composite fiber according to (1), wherein a CV % ofangles formed by neighboring line segments each connecting a middlepoint of an exposed portion of each of the conductive layers on theoutside surface of the conductive composite fiber in a fiber crosssection and a center point of the fiber cross section is 5% or less.(3) The conductive composite fiber according to (1) or (2), wherein thethermoplastic resin contains a polyamide or a polyester.

It is possible to provide a conductive composite fiber in which thevariation in the fiber surface specific resistance is suppressed and thevariation in area of the conductive layers in a fiber cross section issuppressed by exposure of the conductive layers at three or morelocations on the fiber surface, crimping of the original yarn issuppressed by equal disposition, and antistatic performance for wovenand knitted fabrics and carpets is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front sectional view of a main part of the structure of anexemplary composite spinneret for illustrating a method of manufacturingthe conductive composite fiber.

FIGS. 2(a)-2(c) are exemplary schematic views showing a cross section ofthe conductive composite fiber.

DESCRIPTION OF REFERENCE SIGNS

-   1: Measuring plate-   2: Distribution plate-   3: Ejecting plate-   4: Measuring groove A-   5: Measuring groove B-   6: Ejecting hole-   7: Conductive layer-   8: Nonconductive layer

DETAILED DESCRIPTION

The conductive composite fiber is a conductive composite fibercontaining a polymer containing a polyamide resin containing aconductive carbon black as a conductive layer, and a thermoplastic resinas a nonconductive layer.

The polyamide resin used in the conductive layer is not particularlylimited as long as it is a polymer including amide bonds produced byrepeated polycondensation. The polyamide resin may be nylon 6, nylon 66,nylon 12, nylon 610 or the like, or may be a polyamide containing asmall amount of a third component. The conductive carbon black may befurnace black, acetylene black, channel black, ketjen black or the like,and is preferably furnace black having excellent dispersibility.

The thermoplastic resin used in the nonconductive layer is notparticularly limited as long as it is a fiber-forming thermoplasticpolymer, and is preferably a polyamide or a polyester because a polymerhaving poor spinnability has poor process passability. The polyamide isnot particularly limited as long as it is a polymer including amidebonds produced by repeated polycondensation. The polyamide may be nylon6, nylon 66, nylon 12, nylon 610 or the like, or may be a polyamidecontaining a small amount of a third component. Furthermore, thepolyamide may contain a small amount of additive, matting agent and thelike. The polyester is preferably polyethylene terephthalate in which 80mol % or more of repeating units are ethylene terephthalate,polybutylene terephthalate in which 80 mol % or more of repeating unitsare butylene terephthalate, or polytrimethylene terephthalate in which80 mol % or more of repeating units are trimethylene terephthalate.Furthermore, the polyester may be copolymerized with aromaticdicarboxylic acids such as terephthalic acid, isophthalic acid,naphthalene 2,6-dicarboxylic acid, phthalic acid, and 5-sodiumsulfoisophthalic acid, aliphatic dicarboxylic acids such as adipic acidand sebacic acid and the like to such an extent that the fiber-formingproperty inherently possessed by the polyester homopolymer is notimpaired. Furthermore, the polyester may contain a small amount ofadditive, matting agent and the like.

The conductive layers are exposed at three or more locations on theoutside surface of the conductive composite fiber in a fiber crosssection. By the exposure at three or more locations, the variation inthe fiber surface specific resistance can be suppressed, and stablestatic elimination performance can be maintained. When the conductivelayers are exposed at two or less locations, the variation in the fibersurface specific resistance increases, and it is difficult to obtaindesired static elimination performance.

The CV % in area of the conductive layers in a fiber cross section is10% or less. By setting the CV % in such a range, the variation in theconductivity between the conductive layers can be suppressed, thewave-like fine crimping in the longitudinal direction of the yarn can besuppressed, and excellent static elimination performance can be obtainedwhen the conductive composite fiber is used in a woven or knittedfabric. When the CV % in area of the conductive layers exceeds 10%, thevariation in the conductivity between the conductive layers increases,missing occurs in the conductive layer portion when the conductivecomposite fiber is used continuously for a long period of time, andstable static elimination performance cannot be obtained. The CV % ispreferably 8% or less.

The conductive composite fiber has an average value of the volumespecific resistance of 4 log (Ω·cm) or less. By setting the averagevalue of the volume specific resistance to 4 log (Ω·cm) or less, adesired static elimination effect can be obtained, and it is possible toexpand applications of the conductive composite fiber to the field inwhich static elimination performance is strongly desired such as carpetsand work clothes. The average value of the volume specific resistance ispreferably 2 to 3.5 log (Ω·cm).

The means for setting the average value of the volume specificresistance to 4 log (Ω·cm) or less may be any of a method of adjustingthe concentration of the conductive carbon black contained in thepolyamide resin, adjusting the occupancy rate of the conductive layersin the surface area in a fiber cross section and the like. Theconductive carbon black preferably has a specific electrical resistanceof 10⁻³ to 10² (Ω·cm). As is well known, when a carbon black iscompletely dispersed in particles, the conductivity is generally poor.When a carbon black assumes a chain structure called a structure, theconductivity is improved and the carbon black is called a conductivecarbon black. Therefore, in making a polymer conductive with aconductive carbon black, it is important to disperse the carbon blackwithout destroying the structure. As the electric conduction mechanismof the conductive carbon black-containing composite, a carbon blackchain contact and a tunnel effect can be mentioned, and the former ismainly mentioned. Accordingly, the longer the carbon black chain is, andat the higher density the carbon black is present in the polymer, thehigher the contact probability is, and the higher the conductivity is.We found that when the conductive carbon black content is less than 15%by mass, there is almost no effect. When the content is 20% by mass, theconductivity is rapidly improved, and when the content exceeds 40% bymass, the effect is almost saturated. Furthermore, when the contentexceeds 40% by mass, the fluidity of the polymer is poor, and thereforethe concentration of the conductive carbon black is preferably 30 to 40%by mass. The occupancy rate of the conductive layers in the surface areain a fiber cross section is not particularly limited, but is preferably3 to 10% from the viewpoints of spinnability, stretchability, andhigh-order passability. By setting the occupancy rate in such a range,the abrasion resistance with various guides in a yarn-making process anda high-order processing process can be suppressed, and stablespinnability, stretchability, and high-order passability can beobtained.

Furthermore, the CV % of the angle formed by neighboring line segmentseach connecting the middle point of the exposed portion of each of theconductive layers on the outside surface of the conductive compositefiber in a fiber cross section and the center point of the fiber crosssection is preferably 5% or less. By setting the CV % in such a range,the wave-like fine crimping in the longitudinal direction of the yarn inthe conductive composite fiber can be suppressed, more excellent staticelimination performance can be obtained when the conductive compositefiber is used in a woven or knitted fabric, and it is possible to applythe conductive composite fiber to the field in which static eliminationperformance is strongly required such as carpets and dust-proof clothes.The CV % is more preferably 3.5% or less.

Crimping is represented by the crimping rate calculated from thedifference between the fiber length without a load and the fiber lengthwith a load of 0.04 cN/dtex of the conductive composite fiber asdescribed below in EXAMPLES. For example, when the fiber length withouta load is 400 mm, and the fiber length with a load of 0.04 cN/dtex is415 mm, the crimping rate is 3.8%.

It is preferable that the conductive layers be equally disposed in afiber cross section to develop more excellent static eliminationperformance.

To form the cross section of an aspect shown in FIGS. 2(a)-2(c) in whichthe conductive layers are equally disposed in the fiber cross section,for example, it is preferable to use a composite spinneret implementedby the composite spinneret technology described in Japanese PatentLaid-open Publication No. 2011-174215.

Since the conductive layer contains a conductive carbon black at a highconcentration of 30 to 40% based on the polyamide resin depending on thestatic elimination performance, the polymer has reduced fluidity at thetime of melting. When the conductive layer component containing such apolymer having the reduced fluidity is distributed, by using a compositespinneret having a structure in which distribution, merging, andmeasuring are repeated a plurality of times with a merging groove havinga plurality of distribution holes, the conductive layers can be equallydisposed, and the area CV % and the angle CV % can be controlled in suchranges.

The composite spinneret shown in FIG. 1 is incorporated into a spinningpack in a state where mainly three types of members, that is, ameasuring plate 1, a distribution plate 2, and an ejecting plate 3 arestacked in this order from the top, and the pack is used for spinning.

In the spinneret member illustrated in FIG. 1, the measuring plate 1 hasa role of measuring the amount of the polymer per each ejecting hole 6and flowing the polymer into the distribution plate 2. The distributionplate 2 has a role of controlling the composite cross section and thecross-sectional shape in the single fiber cross section, and theejecting plate 3 has a role of compressing and ejecting the compositepolymer flow formed with the distribution plate 2.

Although not shown in FIG. 1 to avoid complicated illustration of thecomposite spinneret, as for the member stacked above the measuring plate1, a member having a channel is required to be used in accordance withthe spinning machine and the spinning pack. By designing the measuringplate 1 in accordance with the existing channel member, the existingspinning pack and members of the spinning pack can be used as they are.Therefore, it is not necessary to dedicate the spinning machineespecially to the spinneret. In practice, a plurality of channel plates(not shown) is preferably stacked between the channel and the measuringplate or between the measuring plate 1 and the distribution plate 2. Thepurpose is to provide a structure with the channel through which thepolymer is transferred and introduced into the distribution plate 2efficiently in the cross-sectional direction of the spinneret and in thecross-sectional direction of the single fiber. The composite polymerflow ejected from the ejecting plate 3 is formed into a composite fiberusing a method in which the composite polymer flow is cooled andsolidified, an oil agent is applied to the composite polymer flow, andan undrawn yarn is wound up once and then heated and drawn in accordancewith a conventional melt spinning method, or a direct spinning drawingmethod in which an undrawn yarn is heated and drawn without being woundup once.

In the manufacture of the conductive composite fiber, it is preferableto control the oxygen concentration immediately below the compositespinneret (ejecting plate 3) to 1% or less. The oxygen concentration (%)is measured using an oxygen concentration meter XP3180E manufactured byNEW COSMOS ELECTRIC CO., LTD. with the tip of a detection tube attachedto the lower surface of the ejecting plate. The oxygen concentration wasmeasured at the following three points, that is, the center of the lowersurface of the ejecting plate, the position of the ejecting hole in theoutermost layer within an area formed by quadrisecting the lower surfaceof the ejecting plate, and the midpoint between the center of the lowersurface of the ejecting plate and the ejecting hole in the outermostlayer, and the number average value was determined. By setting theoxygen concentration in such a range, the effect of suppressingcontamination of the spinneret is exhibited and, as a result, formationof the composite cross section is stabilized. In particular, in apolyamide fiber sensitive in terms of thermal stability and stabilityagainst oxygen, the effect is more remarkable. As a result, theformation stability of the composite cross section over time can bedramatically improved, and the conductive layers can be accuratelyequally disposed.

EXAMPLES

Our fibers and methods are described more specifically with reference toexamples. The physical property values in the examples were measured bythe methods described below.

(1) Fineness (dtex)

The fineness was measured in accordance with JIS L1013 (2010) 8.3.1,Fineness based on Corrected Weight (Method A). The official moistureregain of a polyamide was 4.5%, and the official moisture regain of apolyester was 0.4%.

(2) Volume Specific Resistance

The electrical resistance value (Ω/cm) was measured under conditions ofa temperature of 20° C. and a humidity of 30% RH using asuper-insulation resistance meter (TERAOHMMETER R-503, manufactured byKawaguchi Denki), and applying a voltage of 100 (V) to a fiber having atest length of 10 cm, and the volume specific resistance was calculatedfrom the following formula:

RS=R×D/(L×SG)×10⁻⁶

-   -   RS: Specific resistance (log (Ω·cm))    -   R: Electrical resistance value (Ω)    -   D: Yarn mass (g) per 10000 m    -   L: Test length (cm)    -   SG: Yarn density (g/cm³).

(3) Area CV (%) of Conductive Layers

The cross section of the conductive composite fiber was enlarged 100 to300 times using a digital microscope (VHX-2000) manufactured by KEYENCECORPORATION, the areas of conductive layer parts in a single yarn weremeasured, and the CV value was calculated.

(4) Angle CV (%)

The cross section of the conductive composite fiber was enlarged 100 to300 times using a digital microscope (VHX-2000) manufactured by KEYENCECORPORATION, angles formed by neighboring line segments each connectinga middle point of an exposed portion of each of the conductive layers onthe outside surface of the fiber in the fiber cross section and thecenter point of the fiber cross section in a single yarn (two-dot chainlines in FIGS. 2(a)-2(c)) were measured, and the CV value wascalculated.

(5) Variation in Surface Specific Resistance

A sample to be measured at medium temperature and medium humidity (25°C., relative humidity 60%) was kept in the atmosphere for at least 48hours and then measured. When the yarn was run with a pair of mirrorrollers including a yarn feeding roller and a take-up roller, theresistance value for a length of 10 m was measured with a device inwhich the running yarn was applied to a probe including two rodterminals connected to an insulation resistance meter SM-8220manufactured by HIOKI E.E. CORPORATION between the rollers under theconditions of a rod diameter of 2 mm, a distance of the applied yarnbetween the rod terminals of 2.0 cm, an applied voltage of 100 V, a yarnfeeding speed of 1 m/min, a yarn tension between the rollers of 0.5cN/dtex, and a sampling rate in the insulation resistance system of 1second, and the average [Ω] of the resulting resistance values wasdivided by the distance of the applied yarn between the rod terminals(2.0 cm) to obtain the average resistivity P [Ω/cm]. Furthermore, thestandard deviation Q of all the resistance values obtained at the sametime was calculated and then the coefficient of variation in the averageresistivity CV (CV=Q/P) was calculated from the ratio of P to Q.

(6) Crimping Rate

The fiber length without a load and the fiber length with a load of 0.04cN/dtex of the conductive composite fiber were measured, and thecrimping rate was calculated from the formula below. The resulting valueis rounded off to the first decimal place.

CR=(F2−F1)/F1×100

-   -   CR: Crimping rate (%)    -   F1: Fiber length (mm) without a load    -   F2: Fiber length with a load of 0.04 cN/dtex.

(7) Carpet Evaluation

The conductive composite fiber was mixed with a nylon 6 crimped yarnhaving a total fineness of 2800 dtex with an air nozzle, the resultingcrimped yarn containing the conductive composite fiber was mixed at arate of 1 to 12, the mixture of the resulting crimped yarn and the nylon6 crimped yarn was formed into a tuft having a fabric weight of 400 g/m²and a pile height of 4.0 m, the tuft was cut into a size of 30 cm×30 cmin width, the charging potential was measured 5 times at each level inaccordance with JIS A 1455 (floor rubbing type charging test), and theaverage charging potential of the resulting three charging potentialvalues excluding the maximum and minimum values was determined andevaluated.

-   -   S: Charging potential of −40 V or less    -   A: Charging potential of −41 V to −50 V    -   B: Charging potential of −51 to −60 V    -   C: Charging potential of −61 V or more

Example 1

A nylon-based chip (trade name “CARBOREX NYRON YT-01” manufactured byDIC Corporation) containing 35% by mass of a conductive carbon black wasused as a conductive layer polymer, and a nylon 6 chip was used as anonconductive layer polymer. The chips were melted at a meltingtemperature of 280° C. in individual pressure melters at a ratio of 5%by mass of the conductive layer polymer to 95% by mass of thenonconductive layer polymer, the melted chips were merged into aspinning pack and a spinneret to form a composite, and the composite wasejected from the spinneret so that the conductive layer polymer wasequally disposed and exposed at three locations on the fiber surface. Inthe spinneret used, three types of members, that is, a measuring plate1, a distribution plate 2, and an ejecting plate 3 were stacked in thisorder from the top, and a plurality of distribution plates were stackedto form a fine channel as shown in FIG. 1. Then, with the oxygenconcentration immediately below the spinneret controlled to 1.0% orless, the polymer ejected from the spinneret was cooled with cold air at18° C. and fed with an emulsion oil agent, and then an undrawn yarn wasobtained at a speed of 900 m/min. Subsequently, the undrawn yarn wasaged for 24 hours in an environment of a temperature of 25° C. and ahumidity of 70% and then wound with a drawing machine at a feed rollerspeed of 150 m/min, at a hot plate temperature of 160° C., and at adrawing roller speed of 450 m/min to obtain a conductive composite fiberof 20 dtex-2 filament having conductive layers exposed at threelocations. The obtained conductive composite fiber had a volume specificresistance value of 3.3 log (Ω·cm), an area CV value of conductivelayers of 3.0%, and an angle CV value of 2.0%. As a result of theevaluation using the obtained conductive composite fiber, the variationin the surface specific resistance was 0.306, the crimping rate was2.3%, and the charging potential was also suppressed to −45 V in theconductive performance evaluation on a carpet. The result of the overallevaluation was A and at an acceptable level.

Example 2

A conductive composite fiber was obtained under the same conditions asin Example 1, except that the ratio of the conductive layer polymer waschanged to 3% by mass, the ratio of the nonconductive layer polymer waschanged to 97% by mass, and the number of locations of the exposedconductive layers was changed to six. The obtained conductive compositefiber had a volume specific resistance value of 3.5 log (Ω·cm), an areaCV value of conductive layers of 6.1%, and an angle CV value of 3.1%. Asa result of the evaluation using the obtained conductive compositefiber, the variation in the surface specific resistance can besuppressed to 0.10σ because the number of locations of the exposedconductive layers was changed to six. The crimping rate was at a levelof 2.8%, and the charging potential was also suppressed to −38 V in theconductive performance evaluation on a carpet. The result of the overallevaluation was S and at an acceptable level.

Example 3

A conductive composite fiber was obtained under the same conditions asin Example 1, except that the number of locations of the exposedconductive layers was changed to six. The obtained conductive compositefiber had a volume specific resistance value of 3.2 log (Ω·cm), an areaCV value of conductive layers of 6.0%, and an angle CV value of 3.0%. Asa result of the evaluation using the obtained conductive compositefiber, the variation in the surface specific resistance can besuppressed to 0.10σ because the number of locations of the exposedconductive layers was changed to six. The crimping rate was at a levelof 2.9%, and the charging potential was suppressed to −30 V in theconductive performance evaluation on a carpet. The result of the overallevaluation was S and at an acceptable level.

Example 4

A conductive composite fiber was obtained under the same conditions asin Example 1, except that a nylon-based chip containing 45% by mass of aconductive carbon black was used as a conductive layer polymer, and thenumber of locations of the exposed conductive layers was changed to six.The obtained conductive composite fiber had a volume specific resistancevalue of 1.9 log (Ω·cm), an area CV value of conductive layers of 6.1%,and an angle CV value of 4.9%. As a result of the evaluation using theobtained conductive composite fiber, the variation in the surfacespecific resistance can be suppressed to 0.12σ because the number oflocations of the exposed conductive layers was changed to six. Thecrimping rate was at a level of 4.7% because the melt viscosity of theconductive layer polymer was high, however, the charging potential was−45 V in the conductive performance evaluation on a carpet. The resultof the overall evaluation was A and at an acceptable level.

Example 5

A conductive composite fiber was obtained under the same conditions asin Example 1, except that the ratio of the conductive layer polymer waschanged to 7% by mass, the ratio of the nonconductive layer polymer waschanged to 93% by mass, and the number of locations of the exposedconductive layers was changed to nine. The obtained conductive compositefiber had a volume specific resistance value of 2.8 log (Ω·cm), an areaCV value of conductive layers of 6.7%, and an angle CV value of 3.3%. Asa result of the evaluation using the obtained conductive compositefiber, the variation in the surface specific resistance was a favorableresult of 0.08σ because the number of locations of the exposedconductive layers was changed to nine. The crimping rate was at a levelof 3.3%, and the charging potential was suppressed to −28 V in theconductive performance evaluation on a carpet. The result of the overallevaluation was S and at an acceptable level.

Example 6

A conductive composite fiber was obtained under the same conditions asin Example 1, except that the ratio of the conductive layer polymer waschanged to 10% by mass, the ratio of the nonconductive layer polymer waschanged to 90% by mass, and the number of locations of the exposedconductive layers was changed to 12. The obtained conductive compositefiber had a volume specific resistance value of 2.5 log (Ω·cm), an areaCV value of conductive layers of 8.2%, and an angle CV value of 3.5%. Asa result of the evaluation using the obtained conductive compositefiber, the variation in the surface specific resistance was a favorableresult of 0.06σ because the number of locations of the exposedconductive layers was changed to 12. The crimping rate was at a level of4.9%, and the charging potential was suppressed to −46 V in theconductive performance evaluation on a carpet. The result of the overallevaluation was A and at an acceptable level.

Example 7

A nylon-based chip (trade name “CARBOREX NYRON YT-01” manufactured byDIC Corporation) containing 35% by mass of a conductive carbon black wasused as a conductive layer polymer, and a polyester chip was used as anonconductive layer polymer. The chips were melted at a meltingtemperature of 285° C. in individual pressure melters at a ratio of 5%by mass of the conductive layer polymer to 95% by mass of thenonconductive layer polymer, the melted chips were merged into aspinning pack and a spinneret to form a composite, and the composite wasejected from the spinneret so that the conductive layer polymer wasequally disposed and exposed at three locations on the fiber surface. Inthe spinneret used, three types of members, that is, a measuring plate1, a distribution plate 2, and an ejecting plate 3 were stacked in thisorder from the top, and a fine channel was formed as shown in FIG. 1.Then, with the oxygen concentration immediately below the spinneretcontrolled to 1.0% or less, the polymer ejected from the spinneret wascooled with cold air at 18° C. and fed with an emulsion oil agent, andthen an undrawn yarn was obtained at a speed of 900 m/min. Subsequently,the undrawn yarn was aged for 24 hours in an environment of atemperature of 25° C. and a humidity of 70% and then wound with adrawing machine at a feed roller speed of 135 m/min, at a hot platetemperature of 170° C., and at a drawing roller speed of 400 m/min toobtain a conductive composite fiber of 20 dtex-2 filament havingconductive layers exposed at three locations. The obtained conductivecomposite fiber had a volume specific resistance value of 3.3 log(Ω·cm), an area CV value of conductive layers of 3.1%, and an angle CVvalue of 2.1%. As a result of the evaluation using the obtainedconductive composite fiber, the variation in the surface specificresistance was 0.31σ, the crimping rate was 2.4%, and the chargingpotential was also suppressed to −44 V in the conductive performanceevaluation on a carpet. The result of the overall evaluation was A andat an acceptable level.

Example 8

A conductive composite fiber was obtained under the same conditions asin Example 7, except that the number of locations of the exposedconductive layers was changed to six. The obtained conductive compositefiber had a volume specific resistance value of 3.2 log (Ω·cm), an areaCV value of conductive layers of 6.1%, and an angle CV value of 3.1%. Asa result of the evaluation using the obtained conductive compositefiber, the variation in the surface specific resistance can besuppressed to 0.11σ because the number of locations of the exposedconductive layers was changed to six. The crimping rate was at a levelof 2.9%, and the charging potential was suppressed to −31 V in theconductive performance evaluation on a carpet. The result of the overallevaluation was S and at an acceptable level.

Comparative Example 1

A nylon-based chip (trade name “CARBOREX NYRON YT-01” manufactured byDIC Corporation) containing 35% by mass of a conductive carbon black wasused as a conductive layer polymer, and a nylon 6 chip was used as anonconductive layer polymer. The chips were melted at a meltingtemperature of 280° C. in individual pressure melters at a ratio of 5%by mass of the conductive layer polymer to 95% by mass of thenonconductive layer polymer, the melted chips were merged into aspinning pack and a spinneret to form a composite, and the composite wasejected from the spinneret so that the conductive layer polymer wasequally disposed and exposed at two locations on the fiber surface. Inthe spinneret used, three types of members, that is, a measuring plate1, a distribution plate 2, and an ejecting plate 3 were stacked in thisorder from the top, and a fine channel was formed as shown in FIG. 1.Then, with the oxygen concentration immediately below the spinneretcontrolled to 1.0% or less, the polymer ejected from the spinneret wascooled with cold air at 18° C. and fed with an emulsion oil agent, andthen an undrawn yarn was obtained at a speed of 900 m/min. Subsequently,the undrawn yarn was aged for 24 hours in an environment of atemperature of 25° C. and a humidity of 70% and then wound with adrawing machine at a feed roller speed of 150 m/min, at a hot platetemperature of 160° C., and at a drawing roller speed of 450 m/min toobtain a conductive composite fiber of 20 dtex-2 filament havingconductive layers exposed at two locations. The obtained conductivecomposite fiber had a volume specific resistance value of 3.3 log(Ω·cm), an area CV value of conductive layers of 3.1%, and an angle CVvalue of 2.2%. As a result of the evaluation using the obtainedconductive composite fiber, the variation in the surface specificresistance was 0.426, the crimping rate was 2.4%, and the chargingpotential was as high as −56 V in the conductive performance evaluationon a carpet. The result of the overall evaluation was B and at anunacceptable level.

Comparative Example 2

A conductive composite fiber was obtained under the same conditions asin Comparative Example 1, except that a nylon-based chip containing 20%by mass of a conductive carbon black was used as a conductive layerpolymer, and the number of locations of the exposed conductive layerswas changed to three. The obtained conductive composite fiber had avolume specific resistance value of 4.5 log (Ω·cm), an area CV value ofconductive layers of 2.8%, and an angle CV value of 2.0%. As a result ofthe evaluation using the obtained conductive composite fiber, thevariation in the surface specific resistance was 0.29σ, and the crimpingrate was 2.3%. The charging potential was, however, as high as −65 V inthe conductive performance evaluation on a carpet because the volumespecific resistance was high. The result of the overall evaluation was Band at an unacceptable level.

Comparative Example 3

A conductive composite fiber was obtained under the same conditions asin Comparative Example 1, except that the oxygen concentrationimmediately below the spinneret was changed to 2.0%, and the number oflocations of the exposed conductive layers was changed to six. Theobtained conductive composite fiber had a volume specific resistancevalue of 3.2 log (Ω·cm), an area CV value of conductive layers of 11.0%,and an angle CV value of 6.0%. As a result of the evaluation using theobtained conductive composite fiber, the variation in the surfacespecific resistance was 0.306, the crimping rate was 5.8%, and thecharging potential was as high as −57 V in the conductive performanceevaluation on a carpet. The result of the overall evaluation was B andat an unacceptable level.

Comparative Example 4

A conductive composite fiber was obtained under the same conditions asin Comparative Example 1, except that in the spinneret used, threemembers, that is, a measuring plate, a distribution plate (no stackeddistribution), and an ejecting plate were stacked, and the number oflocations of the exposed conductive layers was changed to six. Theobtained conductive composite fiber had a volume specific resistancevalue of 3.2 log (Ω·cm), an area CV value of conductive layers of 13.0%,and an angle CV value of 7.0%. As a result of the evaluation using theobtained conductive composite fiber, the variation in the surfacespecific resistance was 0.41σ, the crimping rate was 8.1%, and thecharging potential was as high as −70 V in the conductive performanceevaluation on a carpet. The result of the overall evaluation was C andat an unacceptable level.

Comparative Example 5

A nylon-based chip (trade name “CARBOREX NYRON YT-01” manufactured byDIC Corporation) containing 35% by mass of a conductive carbon black wasused as a conductive layer polymer, and a polyester chip was used as anonconductive layer polymer. The chips were melted at a meltingtemperature of 285° C. in individual pressure melters at a ratio of 5%by mass of the conductive layer polymer to 95% by mass of thenonconductive layer polymer, the melted chips were merged into aspinning pack and a spinneret to form a composite, and the composite wasejected from the spinneret so that the conductive layer polymer wasequally disposed and exposed at six locations on the fiber surface. Inthe spinneret used, three members, that is, a measuring plate, adistribution plate (no stacked distribution), and an ejecting plate werestacked. Then, with the oxygen concentration immediately below thespinneret controlled to 1.0% or less, the polymer ejected from thespinneret was cooled with cold air at 18° C. and fed with an emulsionoil agent, and then an undrawn yarn was obtained at a speed of 900m/min. Subsequently, the undrawn yarn was aged for 24 hours in anenvironment of a temperature of 25° C. and a humidity of 70% and thenwound with a drawing machine at a feed roller speed of 135 m/min, at ahot plate temperature of 170° C., and at a drawing roller speed of 400m/min to obtain a conductive composite fiber of 20 dtex-2 filamenthaving conductive layers exposed at six locations. The obtainedconductive composite fiber had a volume specific resistance value of 3.3log (Ω·cm), an area CV value of conductive layers of 12.9%, and an angleCV value of 6.9%. As a result of the evaluation using the obtainedconductive composite fiber, the variation in the surface specificresistance was 0.37σ, the crimping rate was 7.9%, and the chargingpotential was as high as −66 V in the conductive performance evaluationon a carpet. The result of the overall evaluation was C and at anunacceptable level.

TABLE 1-1 Unit Example 1 Example 2 Example 3 Example 4 Example 5 Example6 Example 7 Example 8 Conductive layer — Polyamide Polyamide PolyamidePolyamide Polyamide Polyamide Polyamide Polyamide polymer Nonconductivelayer — Polyamide Polyamide Polyamide Polyamide Polyamide PolyamidePolyester Polyester polymer Number of locations (Location) 3 6 6 6 9 123 6 of exposed conductive layers Average of volume (log(Ω · cm)) 3.3 3.53.2 1.9 2.8 2.5 3.3 3.2 specific resistance Area CV of conductive (%)3.0 6.1 6.0 6.1 6.7 8.2 3.1 6.1 layers Angle CV (%) 2.0 3.1 3.0 4.9 3.33.5 2.1 3.1 Occupancy rate of (%) 5 3 5 5 7 10 5 5 conductive layersVariation in surface (σ) 0.30 0.10 0.10 0.12 0.08 0.06 0.31 0.11specific resistance Crimping rate (%) 2.3 2.8 2.9 4.7 3.3 4.9 2.4 2.9Carpet performance — A S S A S A A S Overall evaluation — A S S A S A AS

TABLE 1-2 Comparative Comparative Comparative Comparative ComparativeUnit Example 1 Example 2 Example 3 Example 4 Example 5 Conductive layer— Polyamide Polyamide Polyamide Polyamide Polyamide polymerNonconductive layer — Polyamide Polyamide Polyamide Polyamide Polyesterpolymer Number of locations (Location) 2 3 6 6 6 of exposed conductivelayers Average of volume (log(Ω · cm)) 3.3 4.5 3.2 3.2 3.3 specificresistance Area CV of conductive (%) 3.1 2.8 11.0 13.0 12.9 layers AngleCV (%) 2.2 2.0 6.0 7.0 6.9 Occupancy rate of (%) 5 5 5 5 5 conductivelayers Variation in surface (σ) 0.42 0.29 0.30 0.41 0.37 specificresistance Crimping rate (%) 2.4 2.3 5.8 8.1 7.9 Carpet performance — BC B C C Overall evaluation — B B B C C

1-3. (canceled)
 4. A conductive composite fiber comprising: a polymer asconductive layers, the polymer containing a polyamide resin containing aconductive carbon black; and a thermoplastic resin as a nonconductivelayer, wherein the conductive layers are exposed at three or morelocations on an outside surface of the conductive composite fiber in afiber cross section, a coefficient of variation (CV %) in area of theconductive layers in a fiber cross section is 10% or less, and theconductive composite fiber has an average value of a volume specificresistance of 4 log (Ω·cm) or less.
 5. The conductive composite fiberaccording to claim 4, wherein a CV % of angles formed by neighboringline segments each connecting a middle point of an exposed portion ofeach of the conductive layers on the outside surface of the conductivecomposite fiber in a fiber cross section and a center point of the fibercross section is 5% or less.
 6. The conductive composite fiber accordingto claim 4, wherein the thermoplastic resin contains a polyamide or apolyester.
 7. The conductive composite fiber according to claim 5,wherein the thermoplastic resin contains a polyamide or a polyester.